Such data storage media can be used, by way of example, in mobile communication systems which are used by mobile subscribers for mobile access. The mobile communication systems comprise the mobile appliance itself and a GSM-specific (Global System for Mobile Communications) data storage medium, known as the SIM (Subscriber Identification Module) unit. A subscriber's SIM unit turns a mobile appliance into a complete mobile communication system, carries secret authentication information for the network operator and additionally contains user-specific data.
The data storage medium is supplied with voltage by means of a battery. To prevent rapid battery exhaustion, power-saving methods are used. If operation of the data storage medium is not required, it can be changed from a normal operating mode to a quiescent mode, known as standby mode. In the quiescent mode, circuit parts of the data storage medium which are not required, such as the CPU, the memory and the peripheral units, can be operated in a mode which results in as low a drawn current as possible. Only the circuit parts which are relevant to activation of the operating mode, for example a communication module and a control unit, remain active and require the full supply of current. Since the time in the quiescent mode in the case of battery-operated data storage media is generally a multiple of the time in the operating mode, this allows the current drawn and hence the maximum power consumption to be minimized in the standby mode and allows considerable extension of the use time of the battery or of the battery's life.
The European Telecommunications Standards Institute (ETSI) is the standardization institute for European telecommunication companies and concerns itself with standardization in the field of European telecommunication. The most important ETSI standard in the field of data storage media is the GSM standards series. “ETSI TS 100 977 V8.3.0 (2000-08) Technical Specification, Digital Cellular Telecommunications Systems (Phase 2+); Specification of the Subscriber Identity Module-Mobile Equipment (SIM-ME) interface (GSM 11.11 version 8.3.0 Release 1999)” describes the specification for communication between SIM card and mobile appliance.
Since the majority of the manufacturers of mobile radios and SIM cards adhere to the specifications cited here when manufacturing the hardware and software for the mobile radios and SIM cards, quasi-standardization has been effected on the market. For the data storage medium or the SIM unit, it is necessary to ensure the demand described in the ETSI on the maximum power consumption in the quiescent mode. In this context, the state of the quiescent mode is defined precisely at the instant at which the data storage medium has transmitted a last item of information or a last byte of a response to a preceding command.
Normally, activation of the quiescent mode after the last item of information has been transmitted requires a series of actions, such as the securing of registers in hardware components and the disconnection of electronic modules from the supply voltage, which result in the maximum power consumption demanded in the standard being exceeded for a defined instant and in the standard being infringed.
New technologies in the manufacture of the data storage media entail higher leakage currents when changing from an operating mode to a subsequent quiescent mode in comparison with previous technologies, which means that the specification regarding maximum power consumption in the quiescent mode is no longer observed.